Cryogenic apparatus

ABSTRACT

A cryogenic apparatus is described which is designed to be of a compact size and to provide multiple functions, including chilling of gas or liquid, condensation of condensible vapors, and separation of liquid and gas phases of liquified cryogenic gas. The level and/or temperature of cryogenic liquid in the apparatus is controlled by sensors. An inlet for liquified cryogenic gas and an inlet for fluid to be chilled or condensed pass through an upper closure and outlets for liquid cryogen and chilled or condensed fluid are provided in the lower wall of the vessel.

REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of copending U.S. patentapplication Ser. No. 506,811 filed Apr. 10, 1990 now abandoned.

FIELD OF INVENTION

The present invention relates to a versatile multifunctional apparatus,particularly useful with cryogenic materials.

BACKGROUND TO THE INVENTION

Cryogenic liquids and gases are well known and are used in a variety ofindustrial applications. A variety of structures has previously beendescribed for storage of such cryogenic materials, separation ofcryogenic gases and liquids and for cooling gases and liquids usingcryogenic materials.

A search conducted in the facilities of the U.S. Patent and TrademarkOffice with respect to the present invention has revealed the followingU.S. Pat. Nos. as the closest prior art:

    ______________________________________                                               4,510,760                                                                            3,422,632                                                              4,607,489                                                                            3,455,117                                                              2,772,545                                                                            3,729,946                                                              3,144,200                                                                            3,913,340                                                              3,296,809                                                                            4,203,299                                                              3,360,947                                                                            4,279,626                                                       ______________________________________                                    

This prior art is illustrative of prior art structures. For reasonswhich will become apparent below, none of this prior art discloses orsuggests the apparatus of the present invention.

In the parent application, the Examiner also has cited the followingU.S. Pat. Nos. as prior art:

    ______________________________________                                               3,049,887                                                                            4,192,147                                                              4,296,610                                                                            4,464,904                                                              4,715,187                                                                            4,726,195                                                       ______________________________________                                    

Of these references, the Examiner has relied mainly on U.S. Pat. Nos.4,296,610 (Davis) and 4,715,187 (Davis). Both of these references relateto subcoolers, whose sole purpose is to reliquify two-phase cryogenicgas, by cooling the two-phase gas with exactly the same gas bath held atnear atmospheric pressure, in which state the gas is the coldestpossible. As will be seen herein, these devices are structurally andfunctionally different from the device provided by the presentinvention.

SUMMARY OF INVENTION

In accordance with the present invention, within a single compactapparatus, multiple functions are obtained. The apparatus of theinvention functions as a chiller to cool gases or liquids to lowtemperatures, as a condenser to condense distillate media or othercondensible vapor to liquid form, and as a phase separator whereby twophase gas-liquid mixtures may be separated for use of either the gas orliquid phase, or both.

Accordingly, in one aspect of the present invention, there is providedan apparatus for handling liquids and gases, which comprises insulatedvessel means having an upper closure and a lower wall and enclosing acooling zone into which a coolant medium may be introduced. First inletmeans communicates through the upper closure with first pipe meansextending within the vessel means through the cooling zone to a firstoutlet means in the lower wall. This arrangement permits a liquid or gasto be passed from the first inlet means to the first outlet means inheat exchange relationship with the cooling zone and to be dischargedfrom the first pipe means through the lower wall.

Second inlet means communicates through the upper closure with pipemeans extending within the vessel means to second outlet means withinthe vessel means whereby a coolant medium may be introduced to thevessel means.

Third outlet means communicates through the lower wall with the coolingzone for discharge of liquid coolant medium from the vessel means bydirect downward flow under the required pressure to a point of use ofthe liquid coolant medium. Fourth outlet means communicates through theupper closure with the cooling zone for discharge of gaseous coolantmedium from the vessel means.

Level control means is provided for controlling the level of liquidcoolant medium in the cooling zone in the vessel means.

In this disclosure, particular emphasis is placed on the use of and theprocessing of cryogenic liquids, since it is these materials with whichthe apparatus of the invention is most useful. However, it will beapparent from the discussion of the construction and operation of thedevice, the invention is useful with other coolant materials. Forexample, when used as a condenser, a cold gas atmosphere may besufficient to effect the desired degree of cooling.

The apparatus of the present invention differs from the prior art in anumber of respects. In this regard, the apparatus possesses a pair ofoutlets in the lower wall, one from the pipe passing through the coolingzone and the other from the cooling zone itself. This arrangementpermits the versatility of operation of the apparatus to act as achiller, a condenser and a phase separator, as well as a source ofcryogenic liquid, to be achieved. Referring to the prior art, as notedpreviously Davis and Stearns are concerned solely with subcoolers toreliquify two-phase cryogenic gas. For this purpose, a body of liquidcryogen at atmospheric pressure is contained in a housing and a coilthrough which the two-phase cryogenic gas is passed is immersed in theliquid cryogen.

The inlet and outlet for the coil both pass through the upper closure tothe vessel. An inlet for liquid cryogen for the body of liquid cryogenalso is provided through the upper closure, feed of such liquid cryogenbeing controlled by a liquid level controller of undisclosed structure.It is not intended that the liquid cryogen be employed other than forthe purpose of subcooling the two-phase cryogenic gas passing throughthe coil nor that the liquid cryogen be maintained at atmosphericpressure.

The Davis device is intended to be comparatively large i.e.approximately 300 Kg when filled, and, therefore, is not easilymountable above the location of the process employing the cryogen. Inthe present invention, in its condenser mode of operation, it isintended that the liquid coolant medium in the apparatus be employedand, for this purpose, is fed from the apparatus through an outlet inthe bottom wall by direct downward flow under the required pressure tothe point of use, conveniently by locating the apparatus above the usepoint. For this purpose, the apparatus has a capacity of about 2 to 3 Kgof gas. This outlet is not a drain, as disclosed in Stearns for emptyingthe apparatus of liquid cryogen, but rather is a functional outletpermitting downstream use of the liquid cryogen, for example, as acoolant in blow-molding operations. For this purpose, the interior ofthe apparatus is maintained under superatmospheric pressure to assist indelivery of the liquid gas to the use point.

A direct downward feed of cryogenic liquified gas is important since anyattempt to deliver liquified gas upward and in cyclical mode (e.g.approximately 20 secs per minute) is thwarted by the accumulation ofvapor at the feed line apex, thereby creating a vapor lock andinhibiting good flow of desired liquid gas.

As noted above, the coil through which the two-phase cryogenic gaspasses in the prior art Davis and Sterns structures both enters andexits through the upper closure to the vessel. In contrast, in theapparatus of the present invention, the coil exits through the bottomwall.

In the condenser or chiller mode of operation, the cooling mediumpresent in the enclosure may be any cold medium which has a sufficientlylow temperature to provide a controlled temperature to any mediumflowing through the heat exchanger coil. For example, the cooling mediummay have a temperature to condense vapors, for example, Freon 12, whichrequires a condensing temperature of -135° C.

It is important that the outlet from the heat-exchanger coil be locatedin the bottom wall of the apparatus, so as to permit condensed orchilled material to drain completely from the coil when flow ceases, soas to avoid freeze up of liquid in the coil.

The present invention also includes the various procedures which areeffected in the apparatus provided in accordance with the one aspect ofthe invention. Accordingly, in another aspect of the invention, there isprovided a method for controlling the flow of cryogenic liquid to an enduse location, which comprises feeding liquified cryogenic gas to anenclosed storage zone and forming a liquid phase and a gaseous phasetherein, discharging the liquid phase by direct downward flow under arequired pressure through a lower outlet from the storage zone,continuously sensing the level of the liquid phase in the storage zone,and controlling the feed of liquified cryogenic gas to the enclosedstorage zone in response to the sensed level of the liquid phase tomaintain a predetermined level of the liquid in the zone.

As will be apparent from the above discussion of the prior art, there isno disclosure in Davis or Stearns of a procedure for controlling theflow of cryogenic liquid to an end use by direct downward flow of liquidphase under a required pressure through a lower outlet. In addition,while the prior art Davis reference discloses monitoring liquid leveland adding additional cryogen as required, this operation is not inresponse to flow of cryogenic liquid from the vessel.

In a further aspect of the invention, there is provided a method forcooling a fluid medium, which comprises flowing the fluid along anenclosed flow path in heat exchange relation with a body ofheat-exchange medium which is capable of removing heat from the fluidand which is located in an enclosed storage zone, the enclosed flow pathextending within the enclosed storage zone from an upper inlet to anlower outlet, and controlling the temperature of fluid exiting theenclosed storage zone at a desired value as a function of flow rate ofthe fluid along the enclosed flow path and the volume of the body ofheat-exchange medium.

Again the prior art does not disclose such a procedure. While Davis andStearns disclose passing a fluid along an enclosed flow path in heatexchange relationship with a liquid cryogen, the enclosed flow path doesnot exit through the bottom closure but rather through the top one andthe purpose in Davis and Stearns is to reliquify two-phase cryogenic gasusing a bath of the same material held at atmospheric pressure. Further,neither Davis nor Stearns discloses a system for control of thetemperature of fluid exiting the enclosed storage zone as a dualfunction of flow rate and volume of heat-exchange medium.

A yet further aspect of the present invention provides a method forcondensing a condensible vapor, which comprises flowing the condensiblevapor along an enclosed flow path in heat exchange relation with a bodyof heat-exchange medium which is capable of removing heat from thecondensible vapor sufficient to condense the same and which is locatedin an enclosed storage zone, the enclosed flow path extending within theenclosed storage zone from an upper inlet to a lower outlet, andcontrolling the temperature of liquid condensate exiting the enclosedstorage zone at a desired value as a function of the temperature of thebody of heat-exchange medium.

The prior art is not concerned with any procedure to effect condensationof condensible vapors to liquid condensate. Davis and Stearns disclose aprocedure for reliquifying two-phase cryogenic gas by passage along anenclosed path in heat exchange relationship with a liquid cryogen, i.e.the same material.

In addition, the flow path exits the subcooler through the upper closurein Davis and Stearns rather than the lower wall, as in the presentinvention. Further, no disclosure exists in the prior art of a procedurefor controlling the temperature of liquid condensate as a function ofthe temperature of the cryogen, or required herein.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is a part sectional view of a cryogenic apparatus provided inaccordance with one embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring to the drawing, a cryogenic apparatus 10 comprises avacuum-insulated vessel 12 of conventional construction and having anupper closure 14. Any other convenient form of insulation may beemployed. The vessel 12 may be constructed to withstand internalpressures up to several hundred psig, depending on its intended use. Afirst upper inlet 16 to the vessel 12 through the upper closure 14 isconnected to a feed line 18 for a liquid or gas to be chilled or avapour to be condensed.

A heat exchanger coil 22 within the vessel 12 connects the first inlet16 to a first outlet 24 in the lower wall 26 of the vessel 12. The heatexchanger coil 22 is partly immersed in a body 28 of cryogenic liquid inthe vessel 12. The first outlet 24 is connected to a feed pipe 30 forconveying chilled liquid or gas or condensed vapour to a use pointthrough a flow control valve 32.

A second upper inlet 34 to the vessel 12 through the upper closure 14 isconnected through a solenoid valve 36 to a feed pipe 38 for a cryogeniccoolant. A pipe 40 inside the vessel 12 is connected to the second inlet34 for discharge of the cryogenic coolant into the vessel 12, through asecond outlet 42, which may take the form of an anti-splash porousfilter 42.

A third lower outlet 44 communicates with the body 28 of cryogenicliquid through the bottom wall 26 of the vessel for discharge of liquidcryogenic material from the vessel through solenoid valve 46 to a feedpipe 48 and thence by direct downward flow under the required pressureto the end use point for the liquid cryogenic material.

A fourth upper outlet 50 communicates through the upper closure 14 tothe vessel 12 with the gas atmosphere 52 above the body 28 of liquidcryogenic material, to enable gas to be discharged through a controlvalve 54 and a check valve 56 to a feed pipe 58 to end use or venting. Asafety pressure relief valve 60 is provided to guard againstoverpressure in the vessel 12. The outlet 50 also is connected throughflow control valve 62 to back pressure adjustment valve 64 to providefor control of internal pressure, as required.

An elongate level control device 68, which may include a thermistor 69at the lower end thereof extends through the top closure 14 to thevessel 12 to communicate with the upper level of the body 28 of liquidin the vessel 12. The thermistor 69 is connected by suitable wiring tothe solenoid valve 36 to control flow in response to electrical signalsfrom the thermistor 69. As soon as the thermistor 69 is covered by theliquid, the coolant in-flow ceases as the solenoid valve 36 is closed.Similarly, when the liquid drops below the thermistor, the solenoidvalve 36 opens and coolant flow recommences. The level control device 68preferably takes the form of a single thermistor sensor packaged into anarrow channel stainless steel tube, so as to minimize heat transferinto the vessel. The vertical position of the level control device isadjustable to provide the required liquid level.

The use of thermistors as level sensors is well known, as indicated bythe Sharp et al reference (U.S. Pat. No. 3,049,887) noted above.However, it is believed that the use of single thermistor 69 for levelcontrol, in contrast to the multiple thermistors in Sharp et al, isunique.

As illustrated, the thermistor 69 is mounted in the tip of the tube 68.When the thermistor 69 is not immersed in liquid nitrogen or othersuitable coolant medium, sufficient heat is carried by conduction of thetubing to warm up the thermistor 69 so that the level controller 68opens the solenoid valve 36 until the thermistor again becomes immersedin liquid nitrogen, so that the valve 36 then is closed.

The stainless steel tubing functions as a delay mechanism so thatopening of the solenoid valve 36 occurs not immediately when thethermistor 69 is immersed in the liquid nitrogen or exposed, but ratheroccurs with a delay that permits level changes of a desired degree, forexample, approximately one inch. This arrangement permits a minimal heatinflux to the cryogen and is beneficial in effecting refills at frequentintervals when operating in the separation mode, so that supply pipingis maintained at a continuous low temperature, so that cryogen warminginside the supply lines is minimized.

A temperature sensor 70 is provided in the outlet pipe 24 from thevessel 12 to sense the temperature therein during operation of thedevice 10 as a condenser, as described in more detail below. Atemperature controller 72 is provided connected by suitable wiring tothe temperature sensor 70 and the solenoid valve 36, to permit operationof the solenoid valve 36 to be controlled directly from the levelcontroller 68 or from the temperature controller 72.

OPERATION

The cryogenic apparatus 10 is capable of multiple functions, namely as achiller, a condenser and a phase separator, as desired. When functioningas a chiller, a gas or liquid to be chilled is passed from the firstinlet 16 to the first outlet 24 through the heat exchanger coil 22. Thebody 28 of cryogenic liquid, such as liquid nitrogen, liquid argon orother liquified gas, cools the liquid or gas as it passes through thecoil 22. In this mode of operation, there is generally a substantiallyuniform flow of liquid or gas through the device 10 which is desired tobe at a specific exit temperature.

The condenser function is similar to the chiller function and isemployed to condense condensible vapours to liquid form. In this mode ofoperation, there is generally a non-uniform flow of condensible vaporsto the device, so that a variable degree of cooling is required. Theoutlet 24 in the lower closure 26 ensures that no liquid is trapped inthe coil 22 when flow to the inlet 16 ceases in either the chiller orcondenser mode of operation.

The exit temperature of the liquid or gas passing through the controlvalve 32 depends upon the level of the body 28 of liquid nitrogen orother coolant medium and the flow rate of the liquid or gas in the heatexchange coil 22. The liquid nitrogen level is determined by the levelcontrol device 68, which may be set at selected heights within thevessel, while the flow rate of the liquid or gas through the heatexchange coil 22 is controlled by the control valve 32. The levelcontrol device 68 controls the solenoid valve 36 to permit additionalcryogenic liquid to be passed into the vessel 12 to maintain the desiredliquid level, as described above.

The temperature sensor 70 senses the temperature of the liquidcondensate in the outlet 24 from the vessel. The temperature is presetto the optimal temperature for condensation of the vapors being treatedin the heat exchanger coil 22 by introduction of the appropriatequantity of cooling medium to the interior of the vessel 10 through pipe40. During passage of the condensible vapor through the coil 22, theinterior temperature of the vessel 10 is sensed indirectly by the sensor70 located in the outlet pipe 24. If the flow rate of condensible gasesbecomes sufficiently high as to cause a rise in temperature in thecondensate, the temperature sensor 70 generates an electrical signalwhich, via controller 72, opens the solenoid valve 36 to permit furthercoolant to enter the vessel 10 to restore the internal temperature tothe desired level, thereby to restore the temperature of condensate tothe desired value. The level controller device 68 is set to its upperextent during the condenser mode and serves to prevent overfilling ofthe vessel 12 by coolant. In this way, the cryogenic apparatus 10 maycontrol precisely the temperatures required to condense a wide range ofvapour distillates.

The phase separation function serves to separate gaseous phase fromliquified cryogenic gases for use of liquid phase, gaseous phase orboth, at various pressures, as required. A two-phase cryogenic mixtureis fed by line 38, through solenoid valve 36, to the interior of thevessel 12, and forms liquid phase 28 and gaseous atmosphere 52. Thesematerials are discharged respectively through outlets 44 and 50 to theirend use points.

One example of the use of the phase separation function is in the blowmolding of plastic containers where nitrogen is required in the liquidphase for efficient cooling. As noted earlier, liquified nitrogen isdifficult to convey upwardly, particularly where short-duration cyclicalinjections are the mode of utilization. During non-flow segments of suchcycles, the liquified gas inside thermally-insulated transfer tubing orhoses partially gasifies, with the gas phase sitting on top of theliquid. When the demand for use initiates, it is only the gas that isavailable initially.

The cryogenic apparatus of the present invention alleviates the problemsince its compact form enables it to be elevated above the use point,thereby enabling delivery by a direct downward flow of liquid under therequired pressure to be effected through outlet 44 and a path for anygas bubbles to escape upwardly by floating upwardly against the downwardliquid flow.

The accumulated gas atmosphere 52 may be employed to supplement theinitial vapour blowing of the parison, so that no gas is wasted in theblow-molding operation.

The cryogenic apparatus of this present invention, therefore, provides aversatility of operation not previously achieved, namely the multiplefunctions of phase separation, chilling and condensation, and providessuch versatility in a compact unit.

SUMMARY OF DISCLOSURE

In summary of this disclosure, the present invention provides a novelcryogenic apparatus which combines the multiple functions of chilling,condensing and phase separation in a single unit by employing a specificarrangement of inlets and outlets in combination with liquid leveland/or temperature control. Modifications are possible within the scopeof this invention.

What I claim is:
 1. A method for cooling a fluid medium, whichcomprises:flowing said fluid along an enclosed flow path in heatexchange relation with a body of heat-exchange medium which is capableof removing heat from said fluid and which is located in an enclosedstorage zone, said enclosed flow path extending within said enclosedstorage zone from an upper inlet to a lower outlet, and controlling thetemperature of fluid exiting said lower outlet of said enclosed flowpath at a desired value as a function of flow rate of said fluid alongsaid enclosed flow path and the volume of said body of heat-exchangemedium.
 2. The method of claim 1 wherein said volume of saidheat-exchange medium in said storage zone in controlled by continuouslysensing the level of liquid heat exchange medium in said enclosedstorage zone and intermittently feeding heat exchange medium to saidenclosed storage zone in response to a sensed level of heat exchangemedium below a predetermined level.
 3. The method of claim 2 whereinsaid flow rate of said fluid along said flow path is controlled by avariable-flow valve means operatively positioned with reference to saidflow path downstream of said enclosed storage zone.
 4. The method ofclaim 3 wherein said fluid is in the form of a liquid or gas flowing ata substantially uniform flow rate along said enclosed flow path.
 5. Themethod of claim 1 wherein said heat exchange medium is a cryogenicliquid.
 6. A method for condensible vapor, which comprises:flowing saidcondensible vapor along an enclosed flow path in heat exchange relationwith a body of heat-exchange medium which is capable of removing heatfrom said condensible vapor sufficient to condense the same and which islocated in an enclosed storage zone, said enclosed flow path extendingwithin said enclosed storage zone from an upper inlet to a lower outlet,and controlling the temperature of liquid condensate exiting said loweroutlet of said enclosed flow path at a desired value as a function ofthe temperature of the body of heat-exchange medium.
 7. The method ofclaim 6 wherein said temperature of said liquid condensate is controlledby continuously sensing the temperature of liquid condensate exitingsaid enclosed storage zone and intermittently feeding heat-exchangemedium to said enclosed storage zone in response to a sensed temperatureof liquid condensate above a predetermined level.
 8. The method of claim7 wherein said condensible vapor flows at a non-uniform flow rate alongsaid enclosed flow path.
 9. The method of claim 6 wherein said heatexchange medium is a cryogenic liquid.